Xcopy in journal based replication

ABSTRACT

A method, system, and program product for data replication, comprising reading do metadata, xcopying data from a storage medium to an undo stream, xcopying data from a do stream to the storage medium, and updating do meta data and the undo meta data.

A portion of the disclosure of this patent document may contain command formats and other computer language listings, all of which are subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.

TECHNICAL FIELD

This invention relates to data replication.

BACKGROUND

Computer data is vital to today's organizations, and a significant part of protection against disasters is focused on data protection. As solid-state memory has advanced to the point where cost of memory has become a relatively insignificant factor, organizations can afford to operate with systems that store and process terabytes of data.

Conventional data protection systems include tape backup drives, for storing organizational production site data on a periodic basis. Such systems suffer from several drawbacks. First, they require a system shutdown during backup, since the data being backed up cannot be used during the backup operation. Second, they limit the points in time to which the production site can recover. For example, if data is backed up on a daily basis, there may be several hours of lost data in the event of a disaster. Third, the data recovery process itself takes a long time.

Another conventional data protection system uses data replication, by creating a copy of the organization's production site data on a secondary backup storage system, and updating the backup with changes. The backup storage system may be situated in the same physical location as the production storage system, or in a physically remote location. Data replication systems generally operate either at the application level, at the file system level, or at the data block level.

Current data protection systems try to provide continuous data protection, which enable the organization to roll back to any specified point in time within a recent history. Continuous data protection systems aim to satisfy two conflicting objectives, as best as possible; namely, (i) minimize the down time, in which the organization production site data is unavailable, during a recovery, and (ii) enable recovery as close as possible to any specified point in time within a recent history.

Continuous data protection typically uses a technology referred to as “journaling,” whereby a log is kept of changes made to the backup storage. During a recovery, the journal entries serve as successive “undo” information, enabling rollback of the backup storage to previous points in time. Journaling was first implemented in database systems, and was later extended to broader data protection.

One challenge to continuous data protection is the ability of a backup site to keep pace with the data transactions of a production site, without slowing down the production site. The overhead of journaling inherently requires several data transactions at the backup site for each data transaction at the production site. As such, when data transactions occur at a high rate at the production site, the backup site may not be able to finish backing up one data transaction before the next production site data transaction occurs. If the production site is not forced to slow down, then necessarily a backlog of un-logged data transactions may build up at the backup site. Without being able to satisfactorily adapt dynamically to changing data transaction rates, a continuous data protection system chokes and eventually forces the production site to shut down.

SUMMARY

A method, system, and program product for data replication, comprising reading do metadata, xcopying data from a storage medium to an undo stream, xcopying data from a do stream to the storage medium, and updating do meta data and the undo meta data.

BRIEF DESCRIPTION OF THE DRAWINGS

Objects, features, and advantages of embodiments disclosed herein may be better understood by referring to the following description in conjunction with the accompanying drawings. The drawings are not meant to limit the scope of the claims included herewith. For clarity, not every element may be labeled in every figure. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments, principles, and concepts. Thus, features and advantages of the present disclosure will become more apparent from the following detailed description of exemplary embodiments thereof taken in conjunction with the accompanying drawings in which:

FIG. 1 is a simplified illustration of a data protection system, in accordance with an embodiment of the present disclosure;

FIG. 2 is a simplified illustration of a write transaction for a journal, in accordance with an embodiment of the present disclosure;

FIG. 3 is a simplified illustration of an xcopy command, in accordance with an embodiment of the present disclosure;

FIG. 4 is a simplified illustration of a DO stream and DO meta data stream, in accordance with an embodiment of the present disclosure;

FIG. 5 is a simplified method using the xcopy command with a DO stream and undo stream, in accordance with an embodiment of the present disclosure;

FIG. 6 is a simplified illustration of using the xcopy command to copy data from a user volume to the undo stream, in accordance with an embodiment of the present disclosure;

FIG. 7 is a simplified illustration of using the xcopy command to copy data from the DO stream to a user volume, in accordance with an embodiment of the present disclosure;

FIG. 8 is a simplified illustration of undo and DO data and a production volume, in accordance with an embodiment of the present disclosure;

FIG. 9 is a simplified method using the xcopy command with a DO stream and undo stream, in accordance with an embodiment of the present disclosure;

FIG. 10 is a simplified illustration of an alternative embodiment of using the xcopy command to copy data from a user volume to the undo stream, in accordance with an embodiment of the present disclosure;

FIG. 11 is a simplified illustration of an alternative embodiment of using the xcopy command to copy data from the DO stream to a user volume, in accordance with an embodiment of the present disclosure;

FIG. 12 is a simplified illustration of undo and DO data with offsets and a production volume, in accordance with an embodiment of the present disclosure;

FIG. 13 is a simplified method using the xcopy command with a DO stream and undo stream, in accordance with an embodiment of the present disclosure;

FIG. 14 is a simplified illustration of using a DO stream with data written to the portion of the user volume, in accordance with an embodiment of the present disclosure;

FIG. 15 is a simplified illustration of DO stream data being transferred to the undo stream, in accordance with an embodiment of the present disclosure; and

FIG. 16 is an example of an embodiment of a method embodied on a computer readable storage medium that may utilize the techniques described herein, in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

Generally, storage arrays are starting to support new types of commands. One such command is the extended copy command (xcopy), which copies data from one volume to another and typically saves host resources and even storage resources. Conventionally, the xcopy command may not immediately copy all of the data from one volume to another and may perform some of the copy on demand.

Thus, replicating the xcopy command is a replication environment may be non-trivial. For example, the source volume may not be replicated, the remote volumes may not be completely in sync, or the remote storage may not support the xcopy command. In some embodiments of the current disclosure, the xcopy command may be replicated in a replication environment with journaling.

In some embodiments, xcopy may be implemented in a journal based replication environment to leverage the journal data. In certain embodiments, the xcopy command may read the target of the xcopy command into the undo stream, and xcopy data from the do stream to the user volume.

The following definitions are employed throughout the specification and claims.

BACKUP SITE—may be a facility where replicated production site data is stored; the backup site may be located in a remote site or at the same location as the production site;

CLONE—a clone may be a copy or clone of the image or images, drive or drives of a first location at a second location;

DELTA MARKING STREAM—may mean the tracking of the delta between the production and replication site, which may contain the meta data of changed locations, the delta marking stream may be kept persistently on the journal at the production site of the replication, based on the delta marking data the DPA knows which locations are different between the production and the replica and transfers them to the replica to make both sites identical.

DPA—may be Data Protection Appliance a computer or a cluster of computers, or a set of processes that serve as a data protection appliance, responsible for data protection services including inter alia data replication of a storage system, and journaling of I/O requests issued by a host computer to the storage system;

RPA—may be replication protection appliance, is another name for DPA.

HOST—may be at least one computer or networks of computers that runs at least one data processing application that issues I/O requests to one or more storage systems; a host is an initiator with a SAN;

HOST DEVICE—may be an internal interface in a host, to a logical storage unit;

IMAGE—may be a copy of a logical storage unit at a specific point in time;

INITIATOR—may be a node in a SAN that issues I/O requests;

JOURNAL—may be a record of write transactions issued to a storage system; used to maintain a duplicate storage system, and to rollback the duplicate storage system to a previous point in time;

LOGICAL UNIT—may be a logical entity provided by a storage system for accessing data from the storage system;

LUN—may be a logical unit number for identifying a logical unit;

PHYSICAL STORAGE UNIT—may be a physical entity, such as a disk or an array of disks, for storing data in storage locations that can be accessed by address;

PRODUCTION SITE—may be a facility where one or more host computers run data processing applications that write data to a storage system and read data from the storage system;

SAN—may be a storage area network of nodes that send and receive I/O and other requests, each node in the network being an initiator or a target, or both an initiator and a target;

SOURCE SIDE—may be a transmitter of data within a data replication workflow, during normal operation a production site is the source side; and during data recovery a backup site is the source side;

SNAPSHOT—a Snapshot may refer to differential representations of an image, i.e. the snapshot may have pointers to the original volume, and may point to log volumes for changed locations. Snapshots may be combined into a snapshot array, which may represent different images over a time period.

STORAGE SYSTEM—may be a SAN entity that provides multiple logical units for access by multiple SAN initiators

TARGET—may be a node in a SAN that replies to I/O requests;

TARGET SIDE—may be a receiver of data within a data replication workflow; during normal operation a back site is the target side, and during data recovery a production site is the target side;

WAN—may be a wide area network that connects local networks and enables them to communicate with one another, such as the Internet.

SPLITTER/PROTECTION AGENT: may be an agent running either on a production host a switch or a storage array which can intercept IO and split them to a DPA and to the storage array, fail IO redirect IO or do any other manipulation to the IO.

VIRTUAL VOLUME: may be a volume which is exposed to host by a virtualization layer, the virtual volume may be spanned across more than one site

DISTRIBUTED MIRROR: may be a mirror of a volume across distance, either metro or geo, which is accessible at all sites.

BLOCK VIRTUALIZATION: may be a layer, which takes backend storage volumes and by slicing concatenation and striping create a new set of volumes, which serve as base volumes or devices in the virtualization layer

MARKING ON SPLITTER: may be a mode in a splitter where intercepted IOs are not split to an appliance and the storage, but changes (meta data) are tracked in a list and/or a bitmap and I/O is immediately sent to down the IO stack.

FAIL ALL MODE: may be a mode of a volume in the splitter where all write and read IOs intercepted by the splitter are failed to the host, but other SCSI commands like read capacity are served.

GLOBAL FAIL ALL MODE: may be a mode of a volume in the virtual layer where all write and read IOs virtual layer are failed to the host, but other SCSI commands like read capacity are served.

LOGGED ACCESS: may be an access method provided by the appliance and the splitter, in which the appliance rolls the volumes of the consistency group to the point in time the user requested and let the host access the volumes in a copy on first write base.

VIRTUAL ACCESS: may be an access method provided by the appliance and the splitter, in which the appliance exposes a virtual volume from a specific point in time to the host, the data for the virtual volume is partially stored on the remote copy and partially stored on the journal.

CDP: Continuous Data Protection, may refer to a full replica of a volume or a set of volumes along with a journal which allows any point in time access, the CDP copy is at the same site, and maybe the same storage array of the production site

CRR: Continuous Remote Replica may refer to a full replica of a volume or a set of volumes along with a journal which allows any point in time access at a site remote to the production volume and on a separate storage array.

As used herein, the term storage medium may refer to one or more storage mediums such as a hard drive, a combination of hard drives, flash storage, combinations of flash storage, combinations of hard drives, flash, and other storage devices, and other types and combinations of computer readable storage mediums including those yet to be conceived. A storage medium may also refer both physical and logical storage mediums and may include multiple level of virtual to physical mappings and may be or include an image or disk image.

A description of journaling and some techniques associated with journaling may be described in the patent titled METHODS AND APPARATUS FOR OPTIMAL JOURNALING FOR CONTINUOUS DATA REPLICATION and with U.S. Pat. No. 7,516,287, which is hereby incorporated by reference.

A discussion of image access may be found in U.S. patent application Ser. No. 12/969,903 entitled “DYNAMIC LUN RESIZING IN A REPLICATION ENVIRONMENT” filed on Dec. 16, 2010 assigned to EMC Corp., which is hereby incorporated by reference.

DESCRIPTION OF EMBODIMENTS USING OF A FIVE STATE JOURNALING PROCESS

Reference is now made to FIG. 1, which is a simplified illustration of a data protection system 100, in accordance with an embodiment of the present invention. Shown in FIG. 1 are two sites; Site I, which is a production site, on the right, and Site II, which is a backup site, on the left. Under normal operation the production site is the source side of system 100, and the backup site is the target side of the system. The backup site is responsible for replicating production site data. Additionally, the backup site enables rollback of Site I data to an earlier pointing time, which may be used in the event of data corruption of a disaster, or alternatively in order to view or to access data from an earlier point in time.

During normal operations, the direction of replicate data flow goes from source side to target side. It is possible, however, for a user to reverse the direction of replicate data flow, in which case Site I starts to behave as a target backup site, and Site II starts to behave as a source production site. Such change of replication direction is referred to as a “failover”. A failover may be performed in the event of a disaster at the production site, or for other reasons. In some data architectures, Site I or Site II behaves as a production site for a portion of stored data, and behaves simultaneously as a backup site for another portion of stored data. In some data architectures, a portion of stored data is replicated to a backup site, and another portion is not.

The production site and the backup site may be remote from one another, or they may both be situated at a common site, local to one another. Local data protection has the advantage of minimizing data lag between target and source, and remote data protection has the advantage is being robust in the event that a disaster occurs at the source side.

The source and target sides communicate via a wide area network (WAN) 128, although other types of networks are also adaptable for use with the present invention.

In accordance with an embodiment of the present invention, each side of system 100 includes three major components coupled via a storage area network (SAN); namely, (i) a storage system, (ii) a host computer, and (iii) a data protection appliance (DPA). Specifically with reference to FIG. 1, the source side SAN includes a source host computer 104, a source storage system 108, and a source DPA 112. Similarly, the target side SAN includes a target host computer 116, a target storage system 120, and a target DPA 124.

Generally, a SAN includes one or more devices, referred to as “nodes”. A node in a SAN may be an “initiator” or a “target”, or both. An initiator node is a device that is able to initiate requests to one or more other devices; and a target node is a device that is able to reply to requests, such as SCSI commands, sent by an initiator node. A SAN may also include network switches, such as fiber channel switches. The communication links between each host computer and its corresponding storage system may be any appropriate medium suitable for data transfer, such as fiber communication channel links.

In an embodiment of the present invention, the host communicates with its corresponding storage system using small computer system interface (SCSI) commands.

System 100 includes source storage system 108 and target storage system 120. Each storage system includes physical storage units for storing data, such as disks or arrays of disks. Typically, storage systems 108 and 120 are target nodes. In order to enable initiators to send requests to storage system 108, storage system 108 exposes one or more logical units (LU) to which commands are issued. Thus, storage systems 108 and 120 are SAN entities that provide multiple logical units for access by multiple SAN initiators.

Logical units are a logical entity provided by a storage system, for accessing data stored in the storage system. A logical unit is identified by a unique logical unit number (LUN). In an embodiment of the present invention, storage system 108 exposes a logical unit 136, designated as LU A, and storage system 120 exposes a logical unit 156, designated as LU B.

In an embodiment of the present invention, LU B is used for replicating LU A. As such, LU B is generated as a copy of LU A. In one embodiment, LU B is configured so that its size is identical to the size of LU A. Thus for LU A, storage system 120 serves as a backup for source side storage system 108. Alternatively, as mentioned hereinabove, some logical units of storage system 120 may be used to back up logical units of storage system 108, and other logical units of storage system 120 may be used for other purposes. Moreover, in certain embodiments of the present invention, there is symmetric replication whereby some logical units of storage system 108 are used for replicating logical units of storage system 120, and other logical units of storage system 120 are used for replicating other logical units of storage system 108.

System 100 includes a source side host computer 104 and a target side host computer 116. A host computer may be one computer, or a plurality of computers, or a network of distributed computers, each computer may include inter alia a conventional CPU, volatile and non-volatile memory, a data bus, an I/O interface, a display interface and a network interface. Generally a host computer runs at least one data processing application, such as a database application and an e-mail server.

Generally, an operating system of a host computer creates a host device for each logical unit exposed by a storage system in the host computer SAN. A host device is a logical entity in a host computer, through which a host computer may access a logical unit. In an embodiment of the present invention, host device 104 identifies LU A and generates a corresponding host device 140, designated as Device A, through which it can access LU A. Similarly, host computer 116 identifies LU B and generates a corresponding device 160, designated as Device B.

In an embodiment of the present invention, in the course of continuous operation, host computer 104 is a SAN initiator that issues I/O requests (write/read operations) through host device 140 to LU A using, for example, SCSI commands. Such requests are generally transmitted to LU A with an address that includes a specific device identifier, an offset within the device, and a data size. Offsets are generally aligned to 512 byte blocks. The average size of a write operation issued by host computer 104 may be, for example, 10 kilobytes (KB); i.e., 20 blocks. For an I/O rate of 50 megabytes (MB) per second, this corresponds to approximately 5,000 write transactions per second.

System 100 includes two data protection appliances, a source side DPA 112 and a target side DPA 124. A DPA performs various data protection services, such as data replication of a storage system, and journaling of I/O requests issued by a host computer to source side storage system data. As explained in detail hereinbelow, when acting as a target side DPA, a DPA may also enable rollback of data to an earlier point in time, and processing of rolled back data at the target site. Each DPA 112 and 124 is a computer that includes inter alia one or more conventional CPUs and internal memory.

For additional safety precaution, each DPA is a cluster of such computers. Use of a cluster ensures that if a DPA computer is down, then the DPA functionality switches over to another computer. The DPA computers within a DPA cluster communicate with one another using at least one communication link suitable for data transfer via fiber channel or IP based protocols, or such other transfer protocol. One computer from the DPA cluster serves as the DPA leader. The DPA cluster leader coordinates between the computers in the cluster, and may also perform other tasks that require coordination between the computers, such as load balancing.

In the architecture illustrated in FIG. 1, DPA 112 and DPA 124 are standalone devices integrated within a SAN. Alternatively, each of DPA 112 and DPA 124 may be integrated into storage system 108 and storage system 120, respectively, or integrated into host computer 104 and host computer 116, respectively. Both DPAs communicate with their respective host computers through communication lines such as fiber channels using, for example, SCSI commands.

In accordance with an embodiment of the present invention, DPAs 112 and 124 are configured to act as initiators in the SAN; i.e., they can issue I/O requests using, for example, SCSI commands, to access logical units on their respective storage systems. DPA 112 and DPA 124 are also configured with the necessary functionality to act as targets; i.e., to reply to I/O requests, such as SCSI commands, issued by other initiators in the SAN, including inter alia their respective host computers 104 and 116. Being target nodes, DPA 112 and DPA 124 may dynamically expose or remove one or more logical units.

As described hereinabove, Site I and Site II may each behave simultaneously as a production site and a backup site for different logical units. As such, DPA 112 and DPA 124 may each behave as a source DPA for some logical units, and as a target DPA for other logical units, at the same time.

In accordance with an embodiment of the present invention, host computer 104 and host computer 116 include protection agents 144 and 164, respectively. Protection agents 144 and 164 intercept SCSI commands issued by their respective host computers, via host devices to logical units that are accessible to the host computers. In accordance with an embodiment of the present invention, a data protection agent may act on an intercepted SCSI commands issued to a logical unit, in one of the following ways:

Send the SCSI commands to its intended logical unit.

Redirect the SCSI command to another logical unit.

Split the SCSI command by sending it first to the respective DPA. After the DPA returns an acknowledgement, send the SCSI command to its intended logical unit.

Fail a SCSI command by returning an error return code.

Delay a SCSI command by not returning an acknowledgement to the respective host computer.

A protection agent may handle different SCSI commands, differently, according to the type of the command. For example, a SCSI command inquiring about the size of a certain logical unit may be sent directly to that logical unit, while a SCSI write command may be split and sent first to a DPA associated with the agent. A protection agent may also change its behavior for handling SCSI commands, for example as a result of an instruction received from the DPA.

Specifically, the behavior of a protection agent for a certain host device generally corresponds to the behavior of its associated DPA with respect to the logical unit of the host device. When a DPA behaves as a source site DPA for a certain logical unit, then during normal course of operation, the associated protection agent splits I/O requests issued by a host computer to the host device corresponding to that logical unit. Similarly, when a DPA behaves as a target device for a certain logical unit, then during normal course of operation, the associated protection agent fails I/O requests issued by host computer to the host device corresponding to that logical unit.

Communication between protection agents and their respective DPAs may use any protocol suitable for data transfer within a SAN, such as fiber channel, or SCSI over fiber channel. The communication may be direct, or via a logical unit exposed by the DPA. In an embodiment of the present invention, protection agents communicate with their respective DPAs by sending SCSI commands over fiber channel.

In an embodiment of the present invention, protection agents 144 and 164 are drivers located in their respective host computers 104 and 116. Alternatively, a protection agent may also be located in a fiber channel switch, or in any other device situated in a data path between a host computer and a storage system.

What follows is a detailed description of system behavior under normal production mode, and under recovery mode.

In accordance with an embodiment of the present invention, in production mode DPA 112 acts as a source site DPA for LU A. Thus, protection agent 144 is configured to act as a source side protection agent; i.e., as a splitter for host device A. Specifically, protection agent 144 replicates SCSI I/O requests. A replicated SCSI I/O request is sent to DPA 112. After receiving an acknowledgement from DPA 124, protection agent 144 then sends the SCSI I/O request to LU A. Only after receiving a second acknowledgement from storage system 108 may host computer 104 initiate another I/O request.

When DPA 112 receives a replicated SCSI write request from data protection agent 144, DPA 112 transmits certain I/O information characterizing the write request, packaged as a “write transaction”, over WAN 128 to DPA 124 on the target side, for journaling and for incorporation within target storage system 120.

DPA 112 may send its write transactions to DPA 124 using a variety of modes of transmission, including inter alia (i) a synchronous mode, (ii) an asynchronous mode, and (iii) a snapshot mode. In synchronous mode, DPA 112 sends each write transaction to DPA 124, receives back an acknowledgement from DPA 124, and in turns sends an acknowledgement back to protection agent 144. Protection agent 144 waits until receipt of such acknowledgement before sending the SCSI write request to LU A.

In asynchronous mode, DPA 112 sends an acknowledgement to protection agent 144 upon receipt of each I/O request, before receiving an acknowledgement back from DPA 124.

In snapshot mode, DPA 112 receives several I/O requests and combines them into an aggregate “snapshot” of all write activity performed in the multiple I/O requests, and sends the snapshot to DPA 124, for journaling and for incorporation in target storage system 120. In snapshot mode DPA 112 also sends an acknowledgement to protection agent 144 upon receipt of each I/O request, before receiving an acknowledgement back from DPA 124.

For the sake of clarity, the ensuing discussion assumes that information is transmitted at write-by-write granularity.

While in production mode, DPA 124 receives replicated data of LU A from DPA 112, and performs journaling and writing to storage system 120. When applying write operations to storage system 120, DPA 124 acts as an initiator, and sends SCSI commands to LU B.

During a recovery mode, DPA 124 undoes the write transactions in the journal, so as to restore storage system 120 to the state it was at, at an earlier time.

As described hereinabove, in accordance with an embodiment of the present invention, LU B is used as a backup of LU A. As such, during normal production mode, while data written to LU A by host computer 104 is replicated from LU A to LU B, host computer 116 should not be sending I/O requests to LU B. To prevent such I/O requests from being sent, protection agent 164 acts as a target site protection agent for host Device B and fails I/O requests sent from host computer 116 to LU B through host Device B.

In accordance with an embodiment of the present invention, target storage system 120 exposes a logical unit 176, referred to as a “journal LU”, for maintaining a history of write transactions made to LU B, referred to as a “journal”. Alternatively, journal LU 176 may be striped over several logical units, or may reside within all of or a portion of another logical unit. DPA 124 includes a journal processor 180 for managing the journal.

Journal processor 180 functions generally to manage the journal entries of LU B. Specifically, journal processor 180 (i) enters write transactions received by DPA 124 from DPA 112 into the journal, by writing them into the journal LU, (ii) applies the journal transactions to LU B, and (iii) updates the journal entries in the journal LU with undo information and removes already-applied transactions from the journal. As described below, with reference to FIGS. 2 and 3A-3D, journal entries include four streams, two of which are written when write transaction are entered into the journal, and two of which are written when write transaction are applied and removed from the journal.

Reference is now made to FIG. 2, which is a simplified illustration of a write transaction 200 for a journal, in accordance with an embodiment of the present invention. The journal may be used to provide an adaptor for access to storage 120 at the state it was in at any specified point in time. Since the journal contains the “undo” information necessary to rollback storage system 120, data that was stored in specific memory locations at the specified point in time may be obtained by undoing write transactions that occurred subsequent to such point in time.

Write transaction 200 generally includes the following fields:

one or more identifiers;

a time stamp, which is the date & time at which the transaction was received by source side DPA 112;

a write size, which is the size of the data block;

a location in journal LU 176 where the data is entered;

a location in LU B where the data is to be written; and

the data itself.

Write transaction 200 is transmitted from source side DPA 112 to target side DPA 124. As shown in FIG. 2, DPA 124 records the write transaction 200 in four streams. A first stream, referred to as a DO stream, includes new data for writing in LU B. A second stream, referred to as an DO METADATA stream, includes metadata for the write transaction, such as an identifier, a date & time, a write size, a beginning address in LU B for writing the new data in, and a pointer to the offset in the do stream where the corresponding data is located. Similarly, a third stream, referred to as an UNDO stream, includes old data that was overwritten in LU B; and a fourth stream, referred to as an UNDO METADATA, include an identifier, a date & time, a write size, a beginning address in LU B where data was to be overwritten, and a pointer to the offset in the undo stream where the corresponding old data is located.

In practice each of the four streams holds a plurality of write transaction data. As write transactions are received dynamically by target DPA 124, they are recorded at the end of the DO stream and the end of the DO METADATA stream, prior to committing the transaction. During transaction application, when the various write transactions are applied to LU B, prior to writing the new DO data into addresses within the storage system, the older data currently located in such addresses is recorded into the UNDO stream.

By recording old data, a journal entry can be used to “undo” a write transaction. To undo a transaction, old data is read from the UNDO stream in a reverse order, from the most recent data to the oldest data, for writing into addresses within LU B. Prior to writing the UNDO data into these addresses, the newer data residing in such addresses is recorded in the DO stream.

The journal LU is partitioned into segments with a pre-defined size, such as 1 MB segments, with each segment identified by a counter. The collection of such segments forms a segment pool for the four journaling streams described hereinabove. Each such stream is structured as an ordered list of segments, into which the stream data is written, and includes two pointers—a beginning pointer that points to the first segment in the list and an end pointer that points to the last segment in the list.

According to a write direction for each stream, write transaction data is appended to the stream either at the end, for a forward direction, or at the beginning, for a backward direction. As each write transaction is received by DPA 124, its size is checked to determine if it can fit within available segments. If not, then one or more segments are chosen from the segment pool and appended to the stream's ordered list of segments.

Thereafter the DO data is written into the DO stream, and the pointer to the appropriate first or last segment is updated. Freeing of segments in the ordered list is performed by simply changing the beginning or the end pointer. Freed segments are returned to the segment pool for re-use.

A journal may be made of any number of streams including less than or more than 5 streams. Often, based on the speed of the journaling and whether the back-up is synchronous or a synchronous a fewer or greater number of streams may be used.

XCOPY (Extended Copy)

XCOPY or extended copy may be a command which copies data from one set of logical units to other logical units, either the same or another set. A device such as a copy manager may perform the XCOPY command. The copy manager may copy data from logical units at the source of the XCOPY command to the destination of the XCOPY command. The logical units or luns may be on the same or different logical or physical devices.

Refer now to the example embodiment of FIG. 3. The example embodiment of FIG. 3 illustrates xcopy command 315 being executed on LUN 320 and LUN 325 on production storage 305. Xcopy 315 indicates a source address and a target address to be copied.

In an embodiment, the current disclosure may replace 4 phases of the aforementioned 5 phase journaling with two extended copy commands. In certain embodiments this may improving the journaling process. In a particular embodiment, the 4 phases replaced may be read data from do stream, read undo data from user volume, write undo data to undo data stream, and write do data to a user volume. In some embodiments, the following may be used reading meta data from do stream (a very small amount of meta data), xcopy data from user volume to undo stream, and xcopy data from do stream to the user volume.

In at least some embodiments, significant bandwidth may be saved between the replication appliance and the storage array. In at least some embodiments, meta data is read through the appliance and the data movement is done within the storage array.

Refer now to the example embodiment of FIG. 4 which illustrates DO meta data stream 410 and DO data stream 432. In this example embodiment DO meta data 410 has a volume information 412, offset information 414, length 416, timestamp t1 418, volume 2 420, offset 2 422, length 2 424 and time t2 426. The DO meta data may also have a bookmark 430. DO data 432 also may contain the DO data such as N1 436 and N2 438. In some embodiments, the DO meta data may contain some of the following: volume information, offsets, lengths, timestamps, and CRC codes. In most embodiments, the DO data represents data that may be written to a user volume and the DO meta data describes meta data or data about the data to be written to the volume.

Refer now to the example embodiment of FIGS. 5, 6, and 7 which illustrate a sample application of xcopy using the DO and UNDO streams. The meta data 635, may be read. Xcopy may copy the information in user volume 620 to the undo stream 640 (step 510). Once data copy from the volumes to the undo stream, Xcopy may copy from the DO stream 730 to the user volume (step 520). The meta data 745 may be updated (step 530) (i.e. the undo stream meta data may be written to the undo meta data stream). The DO data in the DO stream written to the user volume 720 and the associated DO meta data may be erased (step 540).

Refer now to the example embodiments of FIGS. 8, 9, 10, and 11. FIG. 9 illustrates a particular example of application of an xcopy command. Metadata is read (step 905). Data from the user volume, LUN 1020, is copied to the UNDO data stream 1025 (data from volume v1, i.e. LUN 1020, from offset 100, of length 30 is copied to the end of the undo stream, at offset 3100) (step 910). Data from the Do Data stream 1110 is copied to user volume, LUN 1120, (data from offset 10000, in the do stream volume, where do stream currently starts is copied to volume v1 LUN 1120, offset 100) (step 920). The UNDO meta data 1115 is updated (indicating a new IO to LUN 1120 offset 100 and length 30 was added to the undo stream) (step 930). The DO head is moved to position 10030 (step 940). Note, in FIGS. 10 and 11, LUNs 920 and 1020 represent the same LUN at different points in time.

Typically, a system may issue many xcopy commands at the same time, i.e. read a set of meta data entries, and in parallel perform all the xcopy command from the user volume to the undo stream and than from the do stream to the user volumes. Generally, in cases where there are overlaps between IOs in the same batch of IOs, simple xcopy may cause inconsistencies. In an embodiment, the xcopy locations which may be overwritten may be copied from the do stream to the undo stream. The other locations from user volumes may be copied to the undo stream. The changed locations from the do stream may be copied to the volume.

Refer now to the example embodiments of FIGS. 12 and 13. In FIG. 12, Do stream 1210 contains 3 IOs to the same volume, LUN 1220. The three IOs of DO stream 1210 are to offset 10, size 10, offset 100 size 10, and offset 15 size 10. In Undo stream 1225 the data from the LUN 1220 needs to be copied before the data of DO stream 1210 may be executed and applied to the volume. The data of the first IO from the starting at offset 15 is xcopied from do stream 1210 to undo stream 1225 (Step 1305). The data from the LUN 1220 is xcopied to the undo stream 1225 (step 1310). Data from the non intersecting portions of the do stream, and latest version of a location which has intersections in this area in the do stream 1210 is xcopied to the LUN 1220.

In some embodiments, there may be several IOs in the DO stream that may overwrite the same location on the LUN. In certain embodiments, this may be because a portion of the LUN may be continually overwritten with new information. In most embodiments, for each location that would be overwritten, the IOs that will be overwritten may be copied from the DO stream to the correct location in the UNDO stream. In at least some embodiments, this may provide a record of all the changes that occur to a particular location in the journal. In further embodiments, this consistency may enable correct access to any point in time.

In a further embodiment, the do stream may contain a set of IOs and the do meta data may contain a offsets. In this embodiment, there may be three IOs in the do, and three offsets in the do meta data, 10-20, 100-110, and 15-24. In this embodiment, after applying the IOs, the undo meta stream may have the following information: IOs 10-19, 100-109, 15-24 (the same meta data as the do meta stream had before application of the IOs. In this embodiment, this enables a roll back of the data in the volume for each IO, as it was applied at different points in time).

In this embodiment, if the image was rolled back only one IO, there may be offsets 15-24 in the do stream. but the volume must contain offsets 15-19 as they appeared in the do stream before the roll of the 3 IOs above and the data in LUN 1220 as it was before we applied the new data to offsets 20-24, for this reason is we rolled all the 3 IOs above together we should have xcopied offsets 15-19 from the do stream to the undo stream.

Refer now to the example embodiment of FIGS. 14 and 15. In this embodiment, Do meta data 1415 indicates that 4 pieces data in the do stream should be written to location L1 1422 on LUN 1420, currently the value 3 is in at location L1 (note, in this embodiment the do meta data has been simplified to represent only a location, L1; in alternative embodiments L1 may be represented in many different ways including by a series of offsets, or offsets indexed by time). The information in DO meta data 1415 corresponds to 4 separate writes of data in DO stream 1410. To ensure consistency, each of these writes (except the latest one) in the do stream are transferred by xcopy, in order, to the end of the undo stream. As well, the data corresponding to this location on LUN 1420 is also copied to the UNDO stream (including value 3 which represents the previous value of this location on the LUN). As well, in most embodiments, the data will be copied in a consistent time order to enable rollbacks to any point in time. For example, after the xcopy has occurred, undo meta data now contains the L1 location and undo stream 1525 has corresponding data. In certain embodiments, xcopy enables the data in the do stream to be copied to the undo stream, preserving the consistency of the journal at each point in time, and enables only the last write in time to be written to LUN 1522.

The methods and apparatus of this invention may take the form, at least partially, of program code (i.e., instructions) embodied in tangible non-transitory media, such as floppy diskettes, CD-ROMs, hard drives, random access or read only-memory, or any other machine-readable storage medium. When the program code is loaded into and executed by a machine, such as the computer of FIG. 1, the machine becomes an apparatus for practicing the invention. When implemented on one or more general-purpose processors, the program code combines with such a processor to provide a unique apparatus that operates analogously to specific logic circuits. As such a general purpose digital machine can be transformed into a special purpose digital machine. FIG. 16 shows Program Logic 1610 embodied on a computer-readable medium 1430 as shown, and wherein the Logic is encoded in computer-executable code configured for carrying out the reservation service process of this invention and thereby forming a Computer Program Product 1600.

The logic for carrying out the method may be embodied as part of the aforementioned system, which is useful for carrying out a method described with reference to embodiments shown in, for example, FIG. 1 and FIG. 2. For purposes of illustrating the present invention, the invention is described as embodied in a specific configuration and using special logical arrangements, but one skilled in the art may appreciate that the device is not limited to the specific configuration but rather only by the claims included with this specification.

Although the foregoing invention has been described in some detail for purposes of clarity of understanding, it may be apparent that certain changes and modifications may be practiced within the scope of the appended claims. Accordingly, the present implementations are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.

In reading the above description, persons skilled in the art will realize that there are many apparent variations that can be applied to the methods and systems described. Thus it will be appreciated that, in addition to data replication systems, the optimal journaling policy of the present invention has widespread application to journaling systems including database systems and version control systems.

In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It may, however, be evident that various modifications and changes may be made to the specific exemplary embodiments without departing from the broader spirit and scope of the invention as set forth in the appended claims. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. 

What is claimed is:
 1. A system for data replication, the system comprising: a storage medium a do data stream wherein the do data stream contains data corresponding to data of IOs split from a production site; do meta data where the do metadata indicates what data of the do stream should be written to an image to move the image to different points in time; an undo data stream, wherein the undo data stream is a stream that contains data that may be used to roll the image of the storage medium to earlier points in time; undo meta data wherein the undo metadata stream has undo metadata that indicates what data of the do stream should be written to an image to move the image to an earlier point in time; the image on the storage medium; and computer-executable logic operating in memory, wherein the computer-executable program logic is configured for execution of: reading the do metadata stream to determine what data is to be written from the do data stream to the image of the storage medium to move the image to a point in time; xcopying data from the image on the storage medium to the undo data stream using a first xcopy command; wherein the parameters for the first xcopy command are created based on the read do meta data; wherein the read do meta data stream indicates is to be overwritten on the storage medium from the do data stream; xcoping the portion of the do stream determined to be over written by other portions of the do stream to the undo data stream using a second xcopy command; wherein the parameters for the second xcopy command are created based on the data in the do meta data stream to make the data corresponding to the portion of the do stream determined to be over written appear as a set of logical units; xcopying data from the do data stream to the image on the storage medium using an third xcopy command; wherein the parameters for the third xcopy command are created based on what data the read do meta data stream indicates is to be written to the image on the storage medium to make the data from the do data stream appear as a set of logical units, wherein each xcopying is able to copy the data of multiple replicated IOs with a single xcopy command; updating the do meta data in the do metadata stream and updating data the undo meta data in the undo metadata stream to indicate that the xcopying has occurred and the image on the storage medium has been rolled to a new point-in-time.
 2. The system of claim 1 wherein the computer-executable logic further comprises: determining that the do meta data stream contains multiple writes to the same portion of the storage medium; and xcopying a portion of the multiple writes to the same portion of the storage medium from the do stream to the undo stream without writing it to the storage medium; wherein the xcopy command is configured to copy data from one set of logical units to other logical units.
 3. The system of claim 2 wherein the computer-executable logic further comprises: xcoping non duplicated data and a latest version of duplicated data from the storage medium to the undo stream.
 4. The system of claim 2 wherein the computer-executable logic further comprises: xcopying non duplicated data and a latest version of duplicated data from the do stream to the user volume.
 5. The system of claim 2 wherein the computer-executable logic further comprises: updating the undo stream meta data.
 6. The system of claim 2 wherein the computer-executable logic further comprises: erasing the do stream data and the do stream meta data.
 7. The system of claim 1, further comprising synchronously transmitting the do data stream to the replication site.
 8. A computer implemented method for data replication, the method comprising: reading do metadata from a do metadata stream to determine what data is to be written from the do data stream to the image of the storage medium and to determine what portion of the do stream data will be overwritten by other portions of the do stream data, where the do metadata indicates what data from a do data stream moves an image on a storage medium to different points in time, wherein the do data stream contains data corresponding to data of IOs split from a production site; xcopying data from the storage medium to an undo data stream using a first xcopy command; wherein the parameters for the first xcopy command are created based on the read do meta data wherein the read do meta data stream indicates is to be overwritten on the storage medium by data from the do data stream wherein the undo data stream is a stream that contains data that may be used to roll the image of the storage medium to earlier points in time; xcoping the portion of the do stream determined to be over written by other portions of the do stream to the undo data stream using a second xcopy command; wherein the parameters for the second xcopy command are created based on the data in the do meta data stream to make the data corresponding to the portion of the do stream determined to be over written appear as a set of logical units; xcopying data from the do data stream to the image of the storage medium using an third xcopy command; wherein the parameters for the third xcopy command are created based on what data the read do meta data indicates is to be written to the image of the storage medium, wherein each xcopying is able to copy the data of multiple replicated IOs with a single xcopy command; updating do meta data in the do metadata stream and updating data the undo meta data in the undo metadata stream to indicate that the xcopying has occurred and the image on the storage medium has been rolled to a new point-in-time, wherein the undo metadata stream has undo metadata that indicates what portion of the undo data stream is written to the storage medium to roll the image of the storage medium to an earlier point-in-time.
 9. The computer implemented method of claim 8, the method further comprising: determining that the do meta data stream contains multiple writes to the same portion of the storage medium; and xcopying a portion of the multiple writes to the same portion of the storage medium from the do stream to the undo stream without writing it to the storage medium; wherein the xcopy command is configured to copy data from one set of logical units to other logical units.
 10. The computer implemented method of claim 9, the method further comprising: xcoping non duplicated data and a latest version of duplicated data from the storage medium to the undo stream.
 11. The computer implemented method of claim 9, the method further comprising: xcopying non duplicated data and a latest version of duplicated data from the do stream to a user volume.
 12. The computer implemented method of claim 9, the method further comprising: updating the undo stream meta data.
 13. The computer implemented method of claim 9, the method further comprising: erasing the do stream data and the do stream meta data.
 14. The computer implemented method of claim 9, further comprising synchronously transmitting the do data stream to the replication site.
 15. A computer program product for use in replication for comprising: a non-transitory computer readable medium encoded with computer executable program code, the code configured to enable the execution of: reading do metadata from a do metadata stream to determine what data is to be written from the do data stream to the image of the storage medium and to determine what portion of the do stream data will be overwritten by other portions of the do stream data, where the do metadata indicates what data from a do data stream moves an image on a storage medium to different points in time, wherein the do data stream contains data corresponding to data of IOs split from a production site; xcopying data from the storage medium to an undo data stream using a first xcopy command; wherein the parameters for the first xcopy command are created based on the read do meta data; wherein the read do meta data stream indicates is to be overwritten on the storage medium by data from the do data stream wherein the undo data stream is a stream that contains data that may be used to roll the image of the storage medium to earlier points in time; xcoping the portion of the do stream determined to be over written by other portions of the do stream to the undo data stream stream using a second xcopy command; wherein the parameters for the second xcopy command are created based on the data in the do meta data stream to make the data corresponding to the portion of the do stream determined to be over written appear as a set of logical units; xcopying data from the do data stream to the image of the storage medium using an third xcopy command; wherein the parameters for the third xcopy command are created based on what data the read do meta data indicates is to be written to the image of the storage medium, to make the data from the do data stream appear as a set of logical units, wherein each xcopying is able to copy the data of multiple replicated IOs with a single xcopy command; updating do meta data in the do metadata stream and updating data the undo meta data in the undo metadata stream to indicate that the xcopying has occurred and the image on the storage medium has been rolled to a new point-in-time, wherein the undo metadata stream has undo metadata that indicates what portion of the undo data stream is written to the storage medium to roll the image of the storage medium to an earlier point-in-time.
 16. A computer program product of claim 15, the code further configured to enable the execution of: determining that the do meta data stream contains multiple writes to the same portion of the storage medium; and xcopying a portion of the multiple writes to the same portion of the storage medium from the do stream to the undo stream without writing it to the storage medium; wherein the xcopy command is configured to copy data from one set of logical units to other logical units.
 17. A computer program product of claim 16, the code further configured to enable the execution of: xcoping non duplicated data and a latest version of duplicated data from the storage medium to the undo stream.
 18. A computer program product of claim 16, the code further configured to enable the execution of: xcopying non duplicated data and a latest version of duplicated data from the do stream to a user volume.
 19. A computer program product of claim 16, the code further configured to enable the execution of: updating the undo stream meta data.
 20. A computer program product of claim 16, the code further configured to enable the execution of: erasing the do stream data and the do stream meta data. 